In general, dyes have unsatisfactory resistance to light, heat, solvents, and chemicals. On the other hand, pigments involve problems of a lack of dispersion, dispersion stability, transparency, profile sharpness of absorption spectra or transmission spectra, or diffusion. In this respect, Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 proposes a novel coloring material having both an advantage of dyes and an advantage of pigments (good solubility of dyes and good weathering resistance of pigments) through the use of a soluble pigment precursor which can be converted to insoluble pigment particles having a size of nanometers by a chemical, thermal, or photolytic method or by laser or other beam irradiation.
The use of a coloring material disclosed in Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 permits the pigment to be evenly dispersed in high concentration in a polymer layer, but on the other hand, there is a disadvantage that elimination partially occurs due to volatilization of the precursor upon conversion of the soluble pigment precursor in the polymer layer to insoluble pigment particles by chemical, thermal, photolytic, or radiation induced means, leading to an uneven reduction in layer thickness. In the case of the soluble pigment precursor, in general, a bulky functional group is introduced to render the precursor soluble in a solvent, and the elimination of the bulky functional group converts the precursor to an insoluble pigment. This renders the above unfavorable tendency significant. Further, when the eliminated functionality is present in a large amount in the layer, there is a fear of the influence of the functionality. For these reasons, it is difficult to apply the coloring material to the field of applications where dimensional accuracy, particularly good coating smoothness are required, such as color filters.
When the soluble pigment is converted to the insoluble pigment in a solvent before coating formation from the viewpoint of avoiding this problem, the precipitation of the pigment extremely lowers the solubility of the pigment in the solvent, leading to the production of coagulation sediment. Therefore, the storage stability is poor, and the preparation of a highly concentrated solution per se becomes difficult.
Meanwhile, in the case of liquid crystal displays, a liquid crystal material is sealed into a gap of about 1 to 10 μm between glass or other transparent substrates provided with transparent electrodes, and the liquid crystal is aligned in a given direction by a voltage applied across the electrodes to form transparent portions and opaque portions, thereby displaying an image. For color liquid crystal displays, a color filter for three primary colors of light is provided on any one of the transparent electrode substrates, and the three primary colors are added by shutter operation of the liquid crystal to display desired colors.
The color filter used in the color liquid crystal display comprises a transparent substrate, a colored layer, a protective layer, and a transparent conductive layer stacked in that order. The color filter and electrodes or transparent electrodes provided with a thin film transistor, which face colored pixels of three primary colors of RGB, are held while leaving a gap of several μm therebetween, and a liquid crystal material is sealed between the gap to form a liquid crystal display.
The colored pixels provided in the color filter are generally formed of a specific colorant, such as a dye or a pigment, in combination with a suitable resin, a binder, a polymer and/or an additive. Dyes generally have unsatisfactory resistance to light, heat, solvents, and chemicals. On the other hand, pigments involve problems of a lack of dispersion, dispersion stability, transparency, profile sharpness of absorption spectra or transmission spectra, or diffusion. In this respect, Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 proposes a coloring material having both an advantage of dyes and an advantage of pigments (good solubility of dyes and good weathering resistance of pigments) through the use of a soluble pigment precursor which can be converted to insoluble pigment particles having a size of nanometers by chemical, thermal, or photolytic means or by laser or other beam irradiation.
The use of a coloring material disclosed in Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 permits the pigment to be evenly dispersed in high concentration in a polymer layer of the colored layer constituting the color filter, but on the other hand, there is a disadvantage that elimination partially occurs due to volatilization of the precursor upon conversion of the soluble pigment precursor in the polymer layer to insoluble pigment particles by chemical, thermal, photolytic, or radiation induced means, leading to an uneven reduction in layer thickness. In the case of the soluble pigment precursor, in general, a bulky functional group is introduced to render the precursor soluble in a solvent, and the elimination of the bulky functional group converts the precursor to an insoluble pigment. This renders the above unfavorable tendency significant. Further, when the eliminated functionality is present in a large amount in the layer, there is a fear of the influence of the functionality. For these reasons, it is difficult to apply the coloring material to the field of applications where dimensional accuracy, particularly good coating smoothness are required, such as color filters.
When the soluble pigment is converted to the insoluble pigment in a solvent before coating formation from the viewpoint of avoiding this problem, the precipitation of the pigment extremely lowers the solubility of the pigment in the solvent, leading to the production of coagulation sediment. Therefore, the storage stability is poor, and the preparation of a highly concentrated solution per se becomes difficult.